Design of Low-Rise Buildings for Extreme Wind Events

Damages from hurricanes and various windstorm events represent a loss of several billions of dollars in the United States. A loss of $30 billion was attributed to Hurricane Andrew alone in Florida in 1993. In 2004 and 2005, Florida, Louisiana, Mississippi, and other locations in the southeast United States and the Caribbean saw an unprecedented wave of major hurricanes causing great destruction and property damage. This paper discusses the topic of home design for high winds and hurricanes, and sums up a recently completed practical research on this subject.     

Wind Design Problems with Building Structures During Construction

A great deal of damage and loss of property are caused by wind during construction. Partially‐completed structures and temporary works that provide support, access, or protection present the greatest risks. The damaging winds are usually much lower than the design wind loads for completed structures. The design wind speed for short‐term exposure, the drag and shielding coefficients for partially completed structures, and the required temporary strength and stability need to be examined. U.S. building codes and standards provide inadequate or no guidance at all. There is a need to investigate, define, and mitigate the wind‐created risks on construction projects.     

Cost-Benefit Model for the Construction of Tornado Shelters

Tornadoes have been identified as one of the leading causes of death and injuries among natural disasters in the United States. Shelters play an important role in tornado mitigation efforts, since tornado-related mortality and injury rates are higher when tornado shelters are not available. This paper describes a methodology to address the viability of construction of tornado shelters in areas which have significant tornado hazards. A cost-benefit model that estimates the relative advantages of three tornado shelter construction strategies was developed and tested. The model accounts for factors such as probability of tornado occurrence, historical death and injury rates, economic incentives, and local construction and maintenance costs. The implications of factors such as useful life period, discount rate, and occupancy on the viability of the shelter were also studied. Relevance of this model to decision makers, as well as future needs for the model, is discussed.     

Mathematical Model for Design of Mass Dampers for Wind Excited Structures

A state space linear mathematical model oriented to the design of passive and active mass dampers for tall buildings and bridges subjected to the wind action is presented in this paper. The model accounts for an arbitrary number of passive and/or active damping devices positioned at arbitrary points of the structure, as well as for an arbitrary number of structural modes of vibration. The aerodynamic terms of the stiffness and damping matrices are considered following a linearized quasisteady approach. A general discussion on the application of H2/H∞ control techniques to the synthesis of the active mass dampers control law is carried out. For the tuning of the mechanical parameters of passive devices, the problem is reformulated in terms of a decentralized static output feedback control law design problem.     

Estimating Uncertainty in the Extreme Value Analysis of Data Generated by a Hurricane Simulation Model

Extreme value analyses of any environmental phenomenon are fraught with difficulties, but the additional difficulty of collecting reliable data during hurricane events makes their analysis even more complicated. A widely accepted procedure is to use calibrated hurricane models to simulate hurricane events. The simulated data can then be subjected to standard extreme value procedures. The estimation uncertainties which arise from such analyses depend upon (1) the extent to which the hurricane models are physically realistic, (2) the length of the simulated series, which consists of about 1,000 or even 10,000 simulated events, and therefore introduces negligible errors, and (3) the length of the historical record on which the simulations are based, which usually consists of about 50 events. In this paper, we propose the use of resampling schemes in an attempt to obtain some reasonable measure of uncertainties due to the relatively short length of the historical record. An intuitive, “naive” procedure is first described, which leads to an alternative approach that has connections with the statistical procedure of bootstrapping. Standard application of these procedures for extremes induces bias, and we propose a simple, though nonstandard method for reducing this effect. The results are illustrated in detail for a dataset of simulated hurricane wind speeds corresponding to a location in Florida and are also summarized for a sequence of 55 locations along the U.S. Gulf and Atlantic coasts.     

Considerations for Design Criteria for Lunar Structures

The development of design criteria for lunar structures must begin soon in order to establish adequate criteria. Some of the items that need consideration in such criteria are discussed. The categorization of the structures will provide designers with information on the purpose and level of complexity of the structure. Various construction materials and structure types that will be critical for the design of lunar structures, are considered. The environment of the moon and its possible effects on structures are presented and lead to the development of a few load cases that need to be considered in design. A probabilistic format for the criteria and design lifetimes are also discussed.     

New Design Procedure for Wind Uplift Resistance of Architectural Metal Roofing Systems

Currently, there are no Canadian national guidelines for the wind uplift resistance of architectural metal roof systems. Thus, it is difficult to judge their suitability and performance based on a common standard. Given the increasing use of metal roofs, it has been determined that there is a need for the development of a design guide, that would be applicable to all regions of Canada. Metal roofs can be classified into two groups: Structural and architectural. This paper focuses on the wind uplift performance of architectural metal roof systems. Several parameters influence the wind uplift performance of the architectural metal roofs. This study finds that air leakage of the structural deck is one of the significant factors that influences the wind uplift performance. This is based on experimental investigations carried out at the Dynamic Roofing Facility of the National Research Council of Canada, using the Special Interest Group on Dynamic Evaluation of Roofing System dynamic wind test protocol. Architectural roofing panels with three different types of commonly used, seam-interlocking mechanisms (joint details) were investigated. It has been noted that the resistance to wind uplift pressure increases dramatically as the air leakage ratio decreases. A modeling method is also described which quantifies system response by simulating the wind gusts over roof specimens with different leakage ratios that can represent field assemblies. The 1995 National Building Code of Canada was utilized for the estimation of the wind-induced loads and the present study provided extensive experimental data for various systems with each type of seam detail. Based on this analysis, a simplified design procedure was developed. The simplified procedure is presented through case studies of metal roof assemblies located in the Canadian provinces of British Columbia, Ontario, and Quebec.     

Operational Requirements for Long-Span Bridges under Strong Wind Events

In the absence of intensive wind tunnel tests, this study provides an effective and accurate approach to estimate the operational driving speed limit on bridges subjected to different road conditions and wind intensities, through a convenient continuous simulation technique (CSP). A fast and vigorous simulation tool, vehicle performance simulation, is developed to effectively model the performance of vehicles traveling on bridges by considering the interactions between wind, vehicles, and the bridge. The CSP, on the other hand, dramatically reduces the data generation time and makes a reliability analysis of vehicles possible. The application of the proposed method on the Confederation Bridge in Canada is presented as a numerical example. The simulation result overrides the general impression that only high-sided vehicles are sensitive to wind attacks, and this work demonstrates that light-weighted vehicles are also likely to suffer from instability problems on bridges under relatively low wind velocity. In addition, different types of vehicle can undergo different instability mechanisms under the same wind condition and these vehicle instability mechanisms vary with wind velocity.     

Conceptual Design of Unpressurized Shelters on Lunar Surface

Three concepts for the shelters on the moon are presented here. It is envisaged that the first robots will land on the moon and start preparing sites for advanced bases and also for future human presence. These robots will encounter severe radiation and micrometeor hits when they are exposed to the lunar atmosphere. During the period of intense solar radiation these robots have to be temporarily sheltered, since shielding on the robots may not be adequate to protect the instruments. The construction of these shelters has to be performed with very little equipment support. This paper presents concepts and their feasibility analysis for the fabrication of shelters under such stringent constraints.     

Estimation of Probabilistic Extreme Wind Load Effects: Combination of Aerodynamic and Wind Climate Data

A refined full-order method is presented for estimating the extreme wind load effects of rigid structures with given mean recurrence intervals (MRIs) by combining the distributions of annual maximum wind speed and extreme load coefficients. This refined method is capable of dealing with any type of asymptotic extreme value distribution. With this full-order method, the predictions of wind load effects by using distributions of annual maximum wind velocity pressure and wind speed are compared that provide information on the sensitivity of predictions to the upper tail of wind speed distribution. The efficacy of the first-order method is examined. The influences of the type of distributions and the variations of annual maximum wind speed and extreme load coefficient on the predictions are quantified. Finally, the first- and full-order methods are extended to wind load effects of dynamically sensitive structures which facilitate a comprehensive probabilistic analysis as compared to the Monte Carlo simulation schemes used in literature. It is pointed out that 78% fractile extreme load coefficient can be used for defining the characteristic load effects of both rigid and dynamically sensitive structures. The wind load factor is insensitive to the variation of extreme load coefficient. It can be approximately estimated through the wind speed factor and the growth rate of extreme wind load effect with increasing wind speed. The result concerning the wind load factor justifies the advantage of specifying design wind speeds with various MRIs in reducing the uncertainties of design wind loading.     

Case for Enhanced In-Home Protection from Severe Winds

This paper presents the results of a study to investigate methods for providing low-cost protection from hazards associated with tornado strikes or other severe wind events. Included are discussions of physical wind damage, the tornado hazard in the United States, and the relative performance of various physical mitigation measures for existing houses (retrofit options). The results can, however, be extended to new construction, where the incremental costs are expected to be far lower than those associated with modifying existing structures. Three primary tornado hazards are discussed: wind pressures, windborne debris, and falling objects. One of the primary objectives of this study was to develop data on impact resistance of typical construction materials. Impact resistance was defined in terms of both first damage and through-penetration. The results suggest that the impact resistance of walls composed of layers of materials can be estimated by summing the impact resistance of the individual layers. The study also considered, on a limited basis, the threat of falling objects such as trees or large branches. Results suggest that a wall designed to resist debris impact will also exhibit satisfactory performance against tree-fall. This paper provides information that may be useful for people making decisions about whether (and how) to modify their homes to provide an increased level of protection from severe windstorms, but not necessarily at the level specified in the FEMA National Performance Criteria for Tornado Shelters and provided by the FEMA 320 designs.     

Mode Shape Corrections for Wind Load Effects

Traditionally, wind analysis procedures based on the “gust loading factor” approach and experimental techniques involving the high frequency base balance and the “stick-type” aeroelastic model test have assumed ideal structural mode shapes, i.e., linear lateral modes and uniform torsional modes. The influence of nonideal mode shapes manifests itself through modifications in the generalized wind load, the structural displacement, the equivalent static wind load (ESWL), and the attendant influence function. This has led to the introduction of several correction procedures, each focusing on an individual feature of the overall response analysis framework. This paper presents a systematic development of correction procedures in terms of correction factors (CFs) to account for nonideal mode shapes in the formulation of generalized load, analysis of structural response, and the derivation of the ESWL. A parameter study is conducted to examine the significance of CFs in estimating various load effects. It is observed that the influence of a nonideal mode shape is actually negligible for the displacement response and the base bending moment, but not so for other load effects, e.g., the base shear and the generalized wind load. Although the existing procedures are effective in correcting the intended response component, they should not be used indiscriminately for other load effects. This paper also presents a correction procedure for the influence of mode shapes on the ESWLs, a loading format that is very attractive for implementation in codes and standards and design practice as well as for the correct interpretation of wind tunnel measurements.     

Role of Insulation Effectiveness on Fire Resistance of Steel Structures under Extreme Loading Events

Fire performance of steel structures is highly dependent on the effectiveness of applied fire insulation. However, insulation materials are susceptible to damage under extreme loading events. A state-of-the-art review on the role of insulation damage on fire resistance of steel structures is presented. Parametric studies on a six-story steel-framed building were carried out to illustrate the effect of insulation damage on fire response of a steel structure. In the analysis, realistic fire scenarios, loading, and failure criteria were taken into consideration. Analysis results indicate that the fire resistance of a steel-framed structure is significantly influenced by the extent of insulation loss, type of fire scenario, and level of lateral load. Insulation damage causes faster deterioration in the structural response of framed buildings under the combined effect of fire and lateral loading. The need for accounting for any insulation damage, arising under extreme loading events, in fire design of steel-framed structures is highlighted, and a performance-based design strategy incorporating fire resistance analysis is discussed.     

Design and Wind Tunnel Performance Testing of a New Omnidirectional Roof Vent

Low-slope roofs are subjected to potentially high levels of suction pressure as reported by Baskaran and Savage in 2003 in “Wind pressure measurements on full scale flat roofs.” Traditional roof assemblies are prone to failure when the low pressure on the roof surface instigates a transfer of forces to the roof membrane. Existing pressure-equalized roof systems use the power of the wind to transmit low pressure to the space immediately beneath the roof membrane, pulling the membrane down to the roof surface. The object of this study is the design of a wind vent which, when coupled with a single-ply roof membrane in a complete roof assembly, will successfully equalize low pressure throughout the entire field of the roof. The proposed wind vent differs from existing equalizer valves in its use of the Bernoulli effect to create low pressure. The vent is omnidirectional and contains no moving parts. Future study will be required to determine the tributary area of each vent and other roof system parameters.     

Multiparameter Assessment Guide for Emergency Shelters: Disaster Relief Applications

A detailed review was conducted of the building industry to develop a list of viable candidates for use as emergency shelter structures. To facilitate this review, a side-by-side analysis of each system had to be conducted. This analysis was facilitated through a request for proposal in which a prototype building was submitted to each interested group. Each party was required to submit a detailed proposal for review by the research team. The investigative team measured each shelter system against 18 performance parameters, classified as military (end-user), structural, and pass/fail. Four shelter systems provided adequate documentation with respect to structural performance and usage parameters. This paper reports on the results of this investigation and develops a list of general conclusions with respect to available emergency shelter systems. This work was supported by the Center for Disaster Management and Humanitarian Assistance, University of South Florida, under contract from the Office for Naval Research.     

Peak Non-Gaussian Wind Effects for Database-Assisted Low-Rise Building Design

Current procedures for estimating the peaks of the stochastic response of tall buildings to wind are based on the assumption that the response is Gaussian. Those procedures are therefore inapplicable to low-rise buildings, in which time histories of wind-induced internal forces are generally non-Gaussian. In this paper, an automated procedure is developed for obtaining from such time histories sample statistics of internal force peaks for low-rise building design and codification. The procedure is designed for use in software for calculating internal force time series by the database-assisted design approach. A preliminary step in the development of the procedure is the identification of the appropriate marginal probability distribution of the time series using the probability plot correlation coefficient method. The result obtained is that the gamma distribution and a normal distribution are appropriate for estimating the peaks corresponding, respectively, to the longer and shorter tail of the time series’ histograms. The distribution of the peaks is then estimated by using the standard translation processes approach. It is found that the peak distribution can be represented by the Extreme Value Type I (Gumbel) distribution. Because estimates obtained from this approach are based on the entire information contained in the time series, they are more stable than estimates based on observed peaks. The procedure can be used to establish minimum acceptable requirements with respect to the duration and sampling rate of the time series of interest, so that the software used for database-assisted design will be both efficient and accurate.     

Design of Dynamically Wind-Loaded Helical Piers for Small Wind Turbines

The expansion of alternative energy has created a demand for sustainable alternatives for wind turbine foundation design. This study investigates the proposed application of helical piers as foundations for guyed cables of small (1–10-kW) wind towers. Before the foundation system can be implemented, pier response to typical working loads and extreme environmental conditions must be determined. Field conditions were determined by equipping an existing wind tower with accelerometers and load cells while monitoring wind speed to determine tower response. A full-scale testing program was conducted, which simulated dynamic loading conditions based on the tower response. The testing program varied between typical working conditions and extreme load events to determine the critical loading case and creep potential from long-term loading. This paper discusses the effects of dynamic loading on helical pier performance and compares the results to that of uplift prediction methods typically used in helical pier design.     

Development of Fiber-Reinforced Polymer Roof-to-Wall Connection

A significant proportion of damage to buildings in hurricanes occurs owing to weak roof-to-wall connections. The objective of this study was to develop an innovative, efficient, and nonintrusive roof-to-wall connection for wood-frame structures by using high-performance fiber reinforced polymer (FRP) composites. Several connection configurations were developed and tested at the component level under uplift loading. The most feasible configuration was selected and further tested at the component level under lateral loadings. The selected FRP tie system was then tested at a full-scale model designed to represent conventional wood-frame buildings. The objective was to assess the connection’s in situ performance under simulated uplift forces. The results of the full-scale tests were in close agreement with those obtained from the component-level tests. Control tests were also performed to evaluate the load capacity of a typical commercial metallic hurricane clip to facilitate comparison of its results with that of the newly developed FRP tie. The FRP tie system described in this study offers an easy-to-apply, nonintrusive, and viable alternative to existing metal hurricane clips for both new construction and existing structures.     

Wind Tunnel Tests for Wind-Excited Benchmark Building

This paper presents an overview of the wind tunnel studies conducted at the boundary layer wind tunnel facility at the University of Sydney to determine across-wind forces acting on the 76-story 306 m high benchmark building. The paper briefly describes the boundary layer wind tunnel and its special features, and then presents the testing procedures and the methodology used to determine the wind loads acting on a 1:400 model of the building.